Symptom: When I connect to IG_Battlegrounds server with a non-downloaded map (I happen to still have a few given it's a new computer), it starts downloading. Upon reaching 100%, it restarts... I have never seen this earlier, it just appeared suddenly right now, and it occurred for at least two maps.

I've yet to verify whether it's just BG or if all servers behave this way, but I'm hoping this is a known problem and that somebody has a clue about what causes it. Wouldn't be surprised if it's somehow related to Windows 8 (lots of weird crap going on with this OS and Warband, haha).

Happens sometimes that you try to join while a map is just about to end. You start downloading that and before you get into play, the next map starts. In that case you download the first map completely, then start downloading the new one. It might also be due to people successfully polling a new map before you finish downloading the first one.

^ Nah, the restart happened about 5 times. It also happened in two distinct situations: 1) after joining the server initially for a map that I didn't have downloaded (I solved this by waiting), 2) after playing for more than an hour and a map that I didn't have was switched to. Like I said, in both cases it kept restarting to download the same map non-stop, so there's no way this was due to map changing.